The largest attack of the Yemen civil war is underway. Here's everything you need to know.

A Saudi-led alliance began the largest assault of Yemen’s civil war Wednesday with an attack on the critical port city of Hodeidah.

Yemen’s government said the move was designed to “cut off Iran’s hand” that had been supplying weapons to Houthi rebels, but aid agencies warned the attack threatens the lives of up to quarter of a million citizens.

In an operation dubbed “Golden Victory,” warplanes and warships pounded Houthi positions in Hodeidah Wednesday morning, supporting Arab and Yemeni ground troops, who marched on the city from the south and the east.

The bombing started shortly after a government-set deadline expired for the rebels to vacate the city at midnight local time.

A military source speaking to the Saudi-owned Al Arabiya network said a large-scale ground operation supported by the Saudi-led multinational coalition’s aerial and naval cover began marching toward Hodeidah from several directions.

The network reported that violent explosions were heard across the city’s outskirts, while the army announced it had gained control of the southern suburb of Nekhailah.

“(We) have exhausted all peaceful and political solutions to get the Houthi militias out from the Port of Hodeidah,” a statement from Yemen’s government said.

“Liberating the port represents the beginning of the Houthis’ collapse,” the statement added. “It will secure navigation in Bab-el-Mandeb Strait and it will cut off Iran’s hands that have drowned Yemen with weapons that are used to shed the Yemenis’ blood.”

However, humanitarian groups fear the bombing put the lives of up to 250,000 people at immediate risk, as well as threatening millions more who rely on aid delivered via the port city.

Located on the Red Sea, Hodeidah is Yemen’s largest port and home to an estimated 600,000 people. It is also the main entry point for aid to those living in rebel-held areas of the country, which includes the most populated regions, such as the capital Sanaa.

Up to 80 percent of the food, medicine, and fuel aid coming into the famine-ravaged country comes through Hodeidah.

The exiled government claims that Hodeidah is also the primary route through which Iran smuggles weapons to the Houthi rebels, an allegation Iran and the Houthis deny.

These weapons range from assault rifles to ballistic missiles, some of which the U.N. and Western nations claim are used to launch attacks deep into Saudi Arabia, including against its capital Riyadh.

According to the World Health Organization, 8.4 million people live in pre-famine conditions in Yemen, leading the U.N. to label it the “worst humanitarian crisis in the world.”

In recent days, U.N. officials, together with diplomats from the U.S. and U.K., have attempted to bring all parties together to avoid an assault on Hodeidah. Those efforts failed, which could cost countless lives.

“A military assault on the port and the city could put literally hundreds of thousands of people who are already highly vulnerable, who are already in trouble, it could put them into a life-threatening situation,” U.N. Humanitarian coordinator for Yemen Lise Grande told NPR this week.

UNICEF executive director Henrietta Fore warned that up to 300,000 children live in or around Hodeidah as well as millions more who rely on aid that comes through the port. “There are 11 million children in need of humanitarian aid in this war-torn country,” Fore said. “Choking off this lifeline will have devastating consequences for every one of them.”

The Yemen civil war began in 2015, and to date more than 10,000 people have been killed with millions displaced.

The conflict started when Houthi rebels, who champion Yemen's Zaidi Shia Muslim minority, took control of large parts of the country from forces loyal to President Abdrabbuh Mansour Hadi.

READ: The U.S. is deeper into Yemen’s civil war than it wants to admit

A coalition of Arab nations led by Saudi Arabia joined the fight against the Houthi rebels three years ago, and the U.N. has said they bear responsibility for much of the civilian death toll.

The U.S. is officially only playing a supporting role in the Yemen conflict — limited to logistics, intelligence sharing, and the refueling of aircraft — but multiple leaks suggest the U.S. Army’s footprint in Saudi Arabia and Yemen is much greater than officially revealed.

Cover image: Supporters of Yemen's Houthi rebels attend a rally in the coastal town of Hodeidah on April 25, 2018 against the killing their political chief Saleh al-Sammad, in a Saudi-led airstrike.(ABDO HYDER/AFP/Getty Images)